Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$84.86	5.855%	$89.8286	$89.83	$89.85	$89.80
Purchase #2	$169.76	10.493%	$187.5729	$187.57	$187.55	$187.60
Purchase #3	$115.85	7.552%	$124.599	$124.60	$124.60	$124.60
Purchase #4	$84.71	7.770%	$91.292	$91.29	$91.30	$91.30
Purchase #5	$88.75	10.282%	$97.8753	$97.88	$97.90	$97.90
Purchase #6	$32.27	3.701%	$33.4643	$33.46	$33.45	$33.50
Purchase #7	$207.36	12.822%	$233.9477	$233.95	$233.95	$233.90
7 purchase totals =	$783.56		$858.5798	$858.58	$858.60	$858.60